The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to controlling an internal combustion engine upon the failure of a crankshaft position sensor.
Presently, automotive companies manufacture data or target wheels for use with speed sensors to detect the speed, timing, and position of an engine crankshaft and/or a camshaft. As is known in the art of four-cycle internal combustion engines (ICEs), position and timing information for a crankshaft and a camshaft is very important to the application and synchronization of spark and fuel. The crankshaft is actuated by combustion in the pistons, and the camshaft actuates the intake and exhaust valves of the pistons. A camshaft may be used in an overhead valve (OHV) configuration where the valves are actuated via pushrods, or in an overhead cam (OHC) configuration where the valves are acted on directly by the camshaft. The camshaft is driven by the crankshaft through a 1:2 reduction (i.e., two rotations of the crankshaft equal one rotation of the camshaft) and the camshaft speed is one-half that of the crankshaft. The crankshaft and camshaft position, for engine control purposes, are measured at a small number of fixed points, and the number of such measurements may be determined by the number of cylinders in the ICE.
In today""s engine control systems, crankshaft speed supplied by a crankshaft sensor provides position, timing, and/or speed information to an electronic controller for controlling the application of spark and fuel to the cylinders of an ICE. The position and timing (phase) of a first camshaft controlling exhaust valves for a cylinder and/or a second camshaft controlling intake valves for a cylinder in an OHC engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices exist in today""s automotive market that require accurate position and timing information provided by a camshaft position sensor.
A crankshaft or camshaft position sensing system typically includes a variable reluctance or Hall effect sensor positioned to sense the passage of a tooth, tab, and/or slot on a target or data wheel coupled to the crankshaft or camshaft. In a four-cycle ICE, the electronic controller must further differentiate the intake, compression, power, and exhaust strokes since the cylinders will be approaching top dead center (TDC) position during the compression and exhaust phases and approaching bottom dead center (BDC) position during the intake and power phases. Accordingly, the application of fuel and spark in a typical ICE will not be applied until enough position information has been obtained from the crank position sensing systems. Thus, the engine controller must not only determine the TDC and BDC positions of the cylinder but also the state of the engine cycle to control fuel and spark. In the event of a failure of the crankshaft position sensor or system, engine timing must somehow be determined to allow a vehicle to function well enough to travel to a destination where the failure can be fixed.
The present invention comprises a method and apparatus to allow a vehicle engine to operate in the event of a crankshaft sensor failure used in sensing systems common to four cycle ICEs, including but not limited to four-, five-, six- and eight-cylinder engines. The camshaft position sensing system of the present invention, specifically the sensor and target wheel used to provide position information for the camshaft and phasing of the camshaft, may be used to provide timing signals for control of fuel and spark in the event of a crankshaft sensor failure.
The present invention utilizes a 4xc3x97 target wheel cam with four binary (state encoded) base periods for engine cam timing functions. Each semi-period or state is bounded by a rising and falling edge that are a fixed angle before TDC for one or more cylinders of all four, five, six, and eight cylinder engine configurations. For five- or six-cylinder engine configurations, a 4xc3x97 target wheel used in a camshaft sensing system may not provide accurate information on the position of a particular cylinder/piston. If spark is applied too early to a cylinder (the cylinder is over-advanced by 20-30 degrees), a negative torque spike may occur. The negative torque spike can create stress on the crankshaft and be transmitted through the crankshaft to a starter motor. Starter motors are typically mounted by a flange to an engine block and are connected to the crankshaft through a coupling such as a gear box or belt. The negative torque spike created by the mis-timing of fuel and spark to an engine may destroy the starter motor coupling or fracture the engine block.
The present invention utilizes the 4xc3x97 target wheel of the camshaft positioning system to provide backup or redundant information to an engine controller for engine timing. Furthermore, for certain engine types such as five-cylinder or six-cylinder engines, the application of spark and fuel for certain cylinders may be prevented to eliminate a negative torque spike. Fuel and spark are supplied to the engine sequentially, one cylinder at a time. When a position within a 720 degree engine cycle is reached where a fuel injector or ignition event for a cylinder can create an over-advance condition, ignition in that cylinder is prevented by turning off the fuel injector and/or spark ignition device. The absence of fuel and spark to that individual cylinder ensures that the cylinder does not produce any torque, positive or negative. All cylinders that cannot generate the over-advance condition are operated with normal fuel injection and spark events.